Swelling
Swelling is the irreversible formation of folds and waves in flat film material . It can be observed as a phenomenon with thin polypropylene films (from 30 µm and thinner). The causes are e.g. B. in the migration of mineral oil-based printing inks or inorganic substances into the polypropylene matrix or in the lack of waiting time or insufficient drying after the printing process on products that are packaged in the films.